Automatic pipet



June 16, 1964 w. J. HARRISON 3,137,172

I AUTOMATIC PIPET Filed Sept. 8, 1960 INVEN TOR. Walter .1 Herr/son HIS ATTORNEYS June 1964 w. J. HARRISON AUTOMATIC PIPET Filed Sept. 8, 1960 2 Sheets-Sheet 2 Fig.3

]NVEN TOR. Waller .1. Herr/son HIS ATTORNEYS United States Patent ()flice Patented June 16, 1964 3,137,172 AUTOMATIU PWET Walter J. Harrison, Pittsburgh, Pa., assignor to Fisher Scientific Company, Pittsburgh, Pa. Filed Sept. 8, 1960, Ser. No. 54,738 8 Claims. (Cl. 73-4254) This application relates to automatic pipet and more particularly'to mechanism for controlling the supply of liquids to the pipet.

In the chemical industry, it is common to analyze the products produced by different steps in any given process in order to be certain that the process is correctly proceeding. Frequently these analyses are made automatically. Such automatic analyses include automatic titrations in which the reagents are supplied to carefully calibrated pipets and then dispensed to a reaction chamber, the filling and dispensing steps being timed by conventional electric timers or signals received from other elements in the titration apparatus. I have invented mechanism for cutting off the supply of liquid reagent to a pipet when the pipet is filled.

Mechanism for cutting off automatically the supply of liquid reagent to a pipet is known. Such mechanism generally consists in a pair of electrodes which extend into the pipet and which are contacted by the liquid reagent when the desired volume is obtained in the pipet. When the liquid contacts the electrode it completes an electric circuit which actuates a valve motor or a valve solenoid to cut off the supply of liquid reagent to the pipet.

My apparatus has advantages over those heretofore used in that I position electrical control means outside of the liquid in the pipet which is dispensed to a reaction chamber thereby avoiding contamination of the reagent by the material of which the electrodes are made. The control means is independent of any vibration of the pipet which might disturb the liquid level in the pipet and thereby aflect the operation of conventional controls. The control also eliminates the possibility of a drop of reagent remaining bridged across the electrodes of the conventional control after the reagent has been dispensed from the pipet. I have also invented electrical control means which can be actuated by liquids which are clear or opaque and which are conducting or non-conducting.

In the accompanying drawings, I have illustrated certain presently preferred embodiments of my invention in which FIGURE 1 is an elevation view of a pipet embodying my invention;

FIGURE 2 is a side elevation of the apparatus shown in FIGURE 1;

FIGURE 3 is a front elevation of a pipet embodying a modified form of my invention; and

FIGURE 4 is a side view of the apparatus shown in FIGURE 3. Referring to FIGURE 1, there is shown a pipet having a main body 5, having a lower stem 6, to which is attached a three-way valve 7. An inlet passage 8 and an outlet passage 9 are connected alternately to a passage leading to the main body 5 and. within the stem 6 by turning the valve '7. Referring to FIGURE 2, it will be seen that the core 10 of the valve 7 has two diagonally extending passages 11 and 12, and that by turning the core, the passageway within the stem 6 can be connected through the passage 12 to the outlet passage 9 or to the inlet passage s'through the core passage 11. A conventional valve motor or a conventional solenoid is used to turn the core 7 to the proper position. Since. such motors and solenoids are conventional, they are not shown in the drawings. The solenoid or the motor is actuated byfa timer or by a suitable signal from other elements in the titrating apparatus which form no part of the present invention.

The upper end of the pipet also has a stem 13 which reduces in diameter both internally and externally towards its upper end. The inner bore 14 of the stem 13 forms an overflow passage. An overflow chamber 15 is fitted over the stem 13 and surrounds an outlet 16 of the overflow passage 14. As appears in FIGURES l and 2 of the drawing, the overflow chamber 15 extends above and below the outlet 16.

A conduit 17 is connected to the chamber 15 adjacent the bottom thereof to drain liquid from the chamber. The conduit 17 extends first downwardly from the chamber 15 and is then bent first into an upwardly extending U- shaped portion 18, and then into a downwardly extending U-shaped portion 19.

At the top of the overflow chamber 15 there is a reduced portion 20 which is circular in cross section and which extends above the top of the main overflow chamber. A tube clamp 21 is fastened onto the reduced portion 20 and carries a threaded nipple 22 through which an electrode 23 extends. The electrode is carried in a second nipple 24 threaded into the nipple 22 so that by turning the nipple 24, the position of the electrode can be adjusted. As shown in FIGURE 1, the electrode 23' extends into the overflow chamber 15 to a point adjacent the bottom of the chamber so that liquid which flows into the chamber from the outlet 16 of the overflow passage 14 will contact the end of the electrode before the liquid flows out through the conduit 17.

The conduit 17 has a branch 25 which connects into the conduit 17 at approximately the point of junction of the two U-shaped portions 18 and 19 of the conduit 17 and extends vertically upward from the conduit 17. The branch 25 has a tube clip 21 which is the same as the clip 21 on the reduced portion 20 of the main overflow chamber. This coupling supports an electrode 26 which extends along the axis of the branch 25 to approximately the point where the U-shaped portions 18 and 19 join.

The coupling 21 on the reduced portion 20 has a Vent hole 2111 so that liquid may flow out of the overflow chamber 15 when liquid siphons out of the U-shaped portion 18. i

The operation of the pipet will now be described. Upon receipt of a suitable signal, the motor or solenoid which moves the valve core 10 turns 'the core so as to connect inlet passage 8 with the passage in the stem 6. Reagent liquid is then forced into the pipet until the main body 5 is filled and liquid flows out of the overflow passage 14 into the overflow chamber 15. Liquid collected in the overflow chamber 15 will contact the electrode 23 and will flow into the conduit 17. Before liquid flows out of the portion 18 into the portion 19 of the conduit, the reagent will also contact the electrode 26. The electrodes 23 and 26 are part of a circuit which controls the operation of the electrical drive for the valve 7 so when the reagent contacts both the electrodes 23 and 26 a circuit is completed which causes the electric drive for the valve to turn the valve 7 to shut off the valve, or to permit liquid to flow out through the passageway 12 and outlet 9. When the supply of fluid to the pipet is closed as just described, the U-shaped portion 19 of the conduit 17 will siphon liquid reagent out of the overflow chamber 15 and the U-shaped portion 18 thus clearing the control mechanism for a subsequent filling of the pipet.

The pipet is constructed so that it has a very precisely determined volume which volume includes not only the capacity of the main body 5 of the pipet, but also the capacity of the passage within the stem 6 and the capacity of the overflow passage 14. Therefore, when a reagent flows out of the overflow passage 14 and engages both of the electrodes 23 and 26, and when the supply of reagent to the pipet is thereby cut off, the pipet contains a very precisely predetermined volume which can be delivered at will or on signal to a reaction vessel of a titrator.

FIGURES 3 and 4 show an automatic pipet embodying a modified form of my invention. The main body 5 of the pipet, the valve 7 and the overflow passage 14 are the same as the pipet shown in FIGURES 1 and 2. The pipet of FIGURES 3 and 4 differs from that shown in FIG- URES l and 2 in the construction of the overflow chamber and in the electrical control means mounted on the overflow chamber.

Referring to FIGURES 3 and 4, the pipet there shown has an overflow chamber 27 which surrounds and extends above and below the outlet 16 of the overflow passage 14. The chamber 27 has a portion 28 which is reduced in cross section and which extends vertically from the main body of the reaction chamber. Preferably, this reduced portion 28 is cylindrical in section.

The electrical control means is mounted on the reduced portion 23 of the overflow chamber 27. Bakelite mounting block 29 having a transverse passage 39 which fits around the portion 28 of the overflow chamber, the block being held in vertical position on the portion 28 by a plastic set screw 31. The block has two passages, 32 and 33 which are in line with each other and which are both at right angles to and separated by the passage 39 so that the portion 28 of the overflow chamber 27 extendsbetween them. The passage 32 holds a neon bulb 34 and the passage 33 holds a photocell 35 and therefore, light from the bulb 34 passes through the portion 28 of the overflow chamber to the photocell 35.

Preferably the photocell 35 is a cadmium selenide photocell which varies in electrical resistance when light strikes its active surface.

It includes a' The bulb 34 is supplied with a control for an automatic pipet which can be actuated current through a fixed resistance 36 and a variable resistance 37 for reasons which will be hereinafter explained.

A conduit 38 is used to drain reagent from the overflow chamber 27. The conduit is connected to the chamber adjacent the bottom of the chamber and extends vertically. upward therefrom. The upper portion of the conduit 38 is bent into a U-shaped portion 39 to form a siphon for withdrawing liquid from the overflow chamber 27. The center of the highest portion of the U-shaped portion 39 is approximately at the same level as the center line of the passages 32 and 33 for reasons which will also be explained. 1

Liquid reagent is supplied to the pipet in the same manner as has been described with reference to the pipet shown in FIGURES 1 and 2. The reagent overflows from the overflow outlet 16 into the overflow chamber 27 and up into the portion 28 having the reduced cross section. If a clear liquid is being measured, the resistance 37 is adjusted so that the bulb 34 does not give enough light to activate the photocell 35. When the liquid rises in the portion 38 to a point opposite the bulb 34, the liquid acts as a condensing lens for the bulb 34 and focuses light fromthe bulb onto the cell so that light from the bulb will then activate the cell. The resistance of the cell decreases so that a current can pass through it. The cell is connected into a circuit which includes a conventional electronic relay responsive to the change in resistance. The relay actuates the electric valve drive to turn the valve 7 as described with respect to the pipet of FIGURES 1 and 2.

If the reagent liquid being used is opaque, the resistance 37 is set so that the bulb 34 supplies suflicient light to activate the cell 35.- When the liquid rises in the portion 28 to a point opposite the bulb 34, it cuts off the light to the cell and this increases the resistance of the cell. No current then passes through the photocell and the cut-oif of the current canbe used to actuate a conventional electronic relay which, in turn, will actuate a motor or solenoid to turn the valve 7. V

An opaque sleeve 40 is placed around the portion28 above the block 29 to prevent any stray light from activat ing the cell 35, l

by clear or opaque, and conducting or non-conducting reagent liquids and in which the electrical control elements are actuated by the reagents when they are in an overflow chamber rather than in the pipet proper. Therefore, reagent which is delivered from the pipet is not contaminated by contact with the electric control element.

While I have described certain presently preferred embodiments of my invention, it is to be understood that it may be otherwise variously used in the scope of the appended claims.

I claim:

1. In apipet having inlet and outlet passages at one end, an overflow passage at the other end, said overflow passage being at the top of'the pipet'when the pipet is in operative position and an electrically driven valve for controlling the flow of liquid through said inlet passage and said outlet passage, mechanism for shutting off the supply of liquid to the pipet comprising an overflow chamber surrounding and extending above and below the outlet of said overflow passage, electrical circuit control means for said valve mounted on said chamber and so positioned with respect thereto that said means is actuated when the liquid in the chamber reaches a predetermined height to close said valve, and a conduit for withdrawing liquid from said overflow chamber and away from said overflow passage.

2. In a pipet having inlet and outlet passages at one end, an overflow passage at the other end, said overflow passage being atthe top of the pipet when the pipet is in operative position, and an electrically driven valve for controlling the flow of liquid through said inlet passage and said outlet passage, mechanism for shutting off the supply of liquid to the pipet comprising an overflow chamber surrounding and extending above and below the outlet of said overflow passage, a conduit connected to said chamber adjacent the bottom thereof for removing liquid therefrom, said conduit having a U-shaped portion facing downwardly to provide a siphon for draining said overflow chamber after it has filled to a predetermined height, electrical circuit control means for said valve mounted on said chamber and so positioned with respect thereto that said means is actuated when the liquid in the chamber reaches a predetermined height to close said valve.

3. In a pipet having inlet and outlet passages at one end and an overflow passage at the other end, said overflow passage being at the top of the pipet when the pipet is in operative position, and an electrically driven valve for controlling the flow of liquid through said inlet passage and said outlet passage, mechanism for shutting off the supply of liquid to the pipet comprising an overflow chamber surrounding and extending above and below the outlet of said overflow passage, a conduit connected to said chamber adjacent the bottom thereof for removing liquid from said chamber and away from said overflow passage, an electrode having a portion extending into liquid flowing into said chamber from said overflow passage and remaining in said chamber during overflow, and a second electrode mounted on'said conduit at a point removed from said chamber and extending into the interior of the tube atjsaid point to make contact with liquid within the tube during overflow, said electrodes being in an electrical circuit which closes said valve when liquid in said chamber and said conduitcontacts both electrodes.

4. Mechanism for controlling the supply of liquid to a pipet as described in claim 3 in which said conduit has a downwardly extending l J-shaped portion whereby liquid may be siphoned from said chamber and said conduit.

5. Mechanism for controlling the supply of liquid to a pipet as described in claim 3 in which said conduit has a portion bent in the form of a double U, the U portion further removed from said chamber extending downwardly, and in which an electrode extends into the conduit to a point opposite the junction of the two U-shaped portions.

6. In a pipet having inlet and outlet passages at one end and an overflow passage at the other end, said overflow passage being at the top of the pipet when the pipet is in operative position and an electrically driven 'valve for controlling the flow of liquid through said inlet passage and said outlet passage, mechanism for shutting oi? the supply of liquid to the pipet comprising an overflow chamber surrounding and extending above and below the outlet of said overflow passage, said chamber having a portion of reduced cross section extending upwardly above the main body of the chamber, electrical circuit control means for said valve mounted on said reduced portion and positioned to be actuated by the presence of liquid at a predetermined level within the said reduced portion to close said valve, a conduit connected to said chamber adjacent the bottom thereof and extending upwardly beyond the main body of said chamber and thence downwardly to form a U-shaped portion, the central axis of the highest portion of said U-shaped portion being on approximately the same level as said electrical control means when the apparatus is in operative position.

7. Mechanism for controlling the supply of liquid to a pipet as described in claim 6 in which said electrical control means comprises a source of light and a photocell positioned on opposite sides of said reduced portion of the overflow chamber whereby light from said source passes through said reduced portion to the photocell.

8. Mechanism for controlling the supply of liquid to a pipet as described in claim 7 in which the photocell is a photo-resistive cell and in which there is means for varying the intensity of said light source.

References Cited in the file of this patent UNITED STATES PATENTS 2,396,527 Osborne Mar. 12, 1946 2,490,627 Hofberg Dec. 6, 1949 2,697,939 Martin et a1 Dec. 28, 1954 FOREIGN PATENTS 1,179,552 France Dec. 22, 1958 

1. IN A PIPET HAVING INLET AND OUTLET PASSAGES ATA ONE END, AN OVERFLOW PASSAGE AT THE OTHER END, SAID OVERFLOW PASSAGE BEING AT THE TOP OF THE PIPET WHEN THE PIPET IS IN OPERATIVE POSITION AND AN ELECTRICALLY DRIVEN VALVE FOR CONTROLLING THE FLOW OF LIQUID THROUGH SAID INLET PASSAGE AND SAID OUTLET PASSAGE, MECHANISM FOR SHUTTING OFF THE SUPPLY OF LIQUID TO THE PIPET COMPRISING AN OVERFLOW CHAMBER SURROUNDING AND EXTENDING ABOVE AND BELOW THE OUTLET OF SAID OVERFLOW PASSAGE, ELECTRICAL CIRCUIT CONTROL MEANS FOR SAID VALVE MOUNTED ON SAID CHAMBER AND SO POSITIONED WITH RESPECT THERETO THAT SAID MEANS IS ACTUATED WHEN THE LIQUID IN THE CHAMBER REACHES A PREDETERMINED HEIHT TO CLOSE SAID VALVE, AND A CONDUIT FOR WITHDRAWING LIQUID FROM SAID OVERFLOW CHAMBER AND AWAY FROM SAID OVERFLOW PASSAGE. 